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Tourists ride in horse carriages past one of the Great Pyramids in Giza, Egypt, Wednesday, Dec. 12, 2012. An Egyptian opposition alliance urged supporters on Wednesday to vote "No" in the referendum on a disputed constitution but said it may still boycott if its conditions are not met. (AP Photo/Petr David Josek)

Tourists ride in horse carriages past one of the Great Pyramids in Giza, Egypt, Wednesday, Dec. 12, 2012. An Egyptian opposition alliance urged supporters on Wednesday to vote "No" in the referendum on a disputed constitution but said it may still boycott if its conditions are not met. (AP Photo/Petr David Josek)